Commercial and residential buildings account for a large portion of the GHG emissions, which play a key role in climate change. Thus, in order to reduce GHG emissions, it is important to design buildings to be more energy efficient. GHG emission targets will be continuously strengthened in future. On the other hand, constraints resulting from economic crises, and increasing numbers of regulations impact designers' ability to reach given environmental objectives. Thus, it is increasingly difficult to achieve ambitious objectives with limited and decreasing design freedom.
Four obstacles can be identified when trying to integrate climate change issues into architectural pre-design methods. The first obstacle is the lack of publications related to low carbon building references, and which could be used in the design process. There are typically two kinds of publications: those relating mainly to aesthetic solutions, and those relating mainly to ethical problems. Architectural design is an iterative process between problems and solutions. The more iterations, the better the architectural design brief can be designed, for finding a proper solution. Therefore, many types of publications are commonly used as metaphors to transform the design brief into first solutions. Designers commonly prefer aesthetic aspects to ethical aspects. The lack of publications can be explained by the following two reasons:                The recent awareness of climate change limits the number of publications.        The constant progression of climate change objectives quickly renders the few available publications quickly obsolete.        
The second obstacle is the time needed to carry out an environmental assessment. Carrying out a life cycle assessment (LCA) for a building is currently a very time consuming process. LCA, also known as life-cycle analysis, ecobalance, and cradle-to-grave analysis, is a technique for assessing environmental impacts associated with all the stages of a building's life from cradle to grave (i.e. from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, to disposal or recycling). LCA is time consuming, because of the necessity to describe dozens or hundreds of building elements. As a consequence, it reduces the possibility of implementing an iterative process, which is crucial for project quality. Fast feedback about the project assessment can be considered to be the most important feature of a decision-making tool. Mathematical methods have been developed to quickly assess the results of a project, avoiding the need to build performance simulations, and using techniques such as multivariate regression. Although the assessment may be performed quickly, it still does not enable an instantaneous global overview of many variants for a better understanding of the problem.
The third obstacle is the uncertainty about the design at an early stage. At this moment, largely incompatible needs co-exist. While robust and reliable LCA requires a high resolution of details of a building project, early design stage implies a low detail resolution. However, it is necessary to perform an LCA early in the design process. If an LCA is performed late in the design process, it decreases the usability of its results for impacting the design. Thus, performing an LCA at an early design stage remains a real challenge. So far, the main ways of tackling this issue have been the LCA methodology improvement, and simplification by reducing the scope of the analysis (over-simplification) by transforming building components into macro-components (sets of components), and implementing data acquisition with computer aided design tools. However, the end result is not precise enough. Simplified techniques can provide results which deviate by as much as 30% from those of a detailed LCA. Moreover, simplification decreases the usability of the LCA because it would then be more difficult to interpret the results.
The fourth obstacle is the non-reproducibility of LCA results. This is due to the method itself, which allows designers to define their own system boundaries (i.e. how extensive the LCA is) and to choose an LCA database (comprising environmental impacts of individual building elements or systems). Thus, two different designers performing an LCA on the same building will produce two different results if the boundaries and LCA database are not clearly specified in the design brief.
As a conclusion, four main obstacles can be identified, which limit the integration of climate change issues at an early design stage:                the lack of publications about the climate change,        the time required for environmental assessment,        the uncertainties about the design at an early stage, and        the non-reproducibility of the results.        
Currently, known design exploration methods can only cope with a very limited number of design parameters (e.g. seven) quantified to a few levels (e.g. three). These known methods only take into consideration the energy used by a building, but for computational reasons cannot perform an LCA analysis, because this would require taking into account a much higher number of design parameters (e.g. 20, or preferably more). This would lead to billions of design alternatives. Furthermore, most of the current architectural tools guide designers through an optimisation process, assessment after assessment. These tools allow a project to be improved, but they do not allow designers to understand the impact of each design parameter. Furthermore, these tools do not necessary let the designers to choose the most optimum design alternative, based on a multi-criteria approach, which refers not only to the GHG emission performance, but also to social and economic considerations for instance.
It is an object of the present invention to overcome the problems related to the integration of environmental considerations into architectural design aspects at an early design stage.